The present invention relates to an ink supply for an ink-jet printer having a diaphragm pump providing ink from the ink supply to a printhead. More particularly, the present invention relates to a method and apparatus for forming a highly reliable diaphragm pump capable of running repeated cycles without failure.
The use of an ink supply that is separately replaceable from the printhead is disclosed in patent application Ser. No. 08/429,915, now U.S. Pat. No. 5,825,387 entitled "Ink Supply For An Ink-Jet Printer" assigned to the assignee of the present invention. The advantage of this type of ink supply is that it allows the user to replace the ink container without replacing the printhead. The printhead can then be replaced at or near the end of printhead life and not when the ink container is exhausted.
U.S. Ser. No. 08/429,915 discloses the use of an ink container that includes a diaphragm pump. The diaphragm pump is actuated by an actuator associated with the inkjet printer for supplying ink from the ink container to the printhead. The use of a pump associated with the ink container ensures a reliable supply of ink to the ink-jet printhead. An interruption in ink flow to the printhead can result in a reduction in print quality or damage to the printhead. This interruption in the flow of ink to the printhead during operation of the printhead can result in printhead deprime which can result in excessive heating of the printhead. If this printhead heating is severe enough the printhead reliability can be reduced or the printhead can fail. Therefore, it is important that the apparatus used to provide ink from the ink container to the printhead be highly reliable.
The diaphragm pump as disclosed in Serial No. 08/429,915 includes a chassis and a diaphragm attached to the chassis. Engagement of the diaphragm by an actuator varies the volume of the chamber defined by the chassis and diaphragm. Varying the volume of the chamber allows ink to be drawn into the chamber and expelled from the chamber. Ink is drawn into the chamber from an ink reservoir. Ink expelled from the chamber is transferred to the printhead by way of an ink conduit.
patent application Ser. No. 08/846,785, now U.S. Pat. No. 5,854,646 entitled "Diaphragm Pump For Ink Supply", assigned to the assignee of the present invention, discloses the use of an ink container diaphragm pump that makes use of a two-layer diaphragm. The two-layer diaphragm includes a vapor barrier layer for limiting the diffusion of air through the diaphragm into the chamber. A second layer of the diaphragm is an elastomer layer disposed between the chassis and the vapor barrier layer. The elastomer layer limits passage of liquid within the chamber through the diaphragm. The two-layer diaphragm is fastened to a chassis using a crimp cap.
It is important that the diaphragm pump be highly reliable. The diaphragm pump should be capable of operating over a large number of actuation cycles without producing fatigue failures in the diaphragm that may result in ink leakage. In addition, the diaphragm should be strong and resistant to rupturing if the ink container is dropped.
The diaphragm on the diaphragm pump should be flexible so that the force required to activate the pump is relatively low. The use of a lower activation force diaphragm pump allows the use of actuators that have lower output force capability. These lower output force actuators tend to be lower cost than actuators having higher output force requirements, reducing the cost of the printing system. In addition, the use of lower force actuators tends to reduce the cost of a retention system used to secure the ink container to the printer. The use of lower cost retention systems tends to reduce the cost of the printing system.
The diaphragm should also be a good barrier for both liquid and gas. It is important that the diaphragm prevent water within the ink from evaporating through the diaphragm altering the viscosity of the ink. In addition, it is important that air be prevented from permeating through the diaphragm producing air bubbles inside the chamber. These air bubbles tend to reduce the pump efficiency as well as introduce air bubbles to the printhead. Air bubbles once in the printhead may enter an ink ejection chamber reducing the volume of ink in the ejection chamber. If sufficient displacement of ink occurs print quality can be reduced as well as a reduction in printhead cooling can occur. This reduction in cooling can result in overheating of the resistive heating element that if severe enough can result in a catastrophic failure of the heating element.
Finally, the diaphragm pump should provide a consistent discharge volume. This discharge volume should have little variation from ink container to ink container. In addition, the diaphragm pump should be well suited for high volume manufacturing techniques allowing the ink container to be produced at lower cost.